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NASA NTRS1976

Selected fretting-wear-resistant coatings for titanium - 6-percent-aluminum - 4-percent-vanadium alloy

A titanium - 6-percent-aluminum - 4-percent-vanadium alloy (Ti-6Al-4V) was subjected to fretting-wear exposures against uncoated Ti-6Al-4V as a baseline and against various coatings and surface treatments applied to Ti-6Al-4V. The coatings evaluated included plasma-sprayed tungsten carbide with 12 percent cobalt, aluminum oxide with 13 percent titanium oxide, chromium oxide, and aluminum bronze with 10 percent aromatic polyester; polymer-bonded polyimide, polyimide with graphite fluoride, polyimide with molybdenum disulfide (MoS2), and methyl phenyl silicone bonded MoS2, preoxidation surface treatment, a nitride surface treatment, and a sputtered MoS2 coating. Results of wear measurements on both the coated and uncoated surfaces after 300,000 fretting cycles indicated that the polyimide coating was the most wear resistant and caused the least wear to the uncoated mating surface.

Bill, R. C.↗

NASA NTRS1978

Sputtering technology in solid film lubrication

Potential and present sputtering technology is discussed as it applies to the deposition of solid film lubricants particularly MoS2, WS2, and PTFE. Since the sputtered films are very thin, the selection of the sputtering parameters and substrate condition is very critical as reflected by the lubricating properties. It was shown with sputtered MoS2 films that the lubricating characteristics are directly affected by the selected sputtering parameters (power density, pressure, sputter etching, dc-biasing, etc.) and the substrate temperature, chemistry, topography and the environmental conditions during the friction tests. Electron microscopy and other surface sensitive analytical techniques illustrate the resulting changes in sputtered MoS2 film morphology and chemistry which directly influence the film adherence and frictional properties.

Spalvins, T.↗

NASA NTRS1978

Sputtering technology in solid film lubrication

Current and potential sputtering technology is reviewed as it applies primarily to the deposition of MoS2, though such lubricants as WS2 and PTFE are also considered. It is shown by electron microscopy and surface sensitive analytical techniques that the lubricating properties of sputtered MoS2 films are directly influenced by the sputtering parameters selected (i.e., power density, pressure, sputter etching, dc-biasing, etc.), substrate temperature, chemistry, topography, and environmental conditions during the friction test. Electron micrographs and diffractograms of sputtered MoS2 films clearly show the resultant changes in film morphology which affect film adherence and frictional properties.

Spalvins, T.↗

NASA NTRS1980

Tribological properties of sputtered MoS sub 2 films in relation to film morphology

Thin sputter deposited MoS2 films in the 2000 to 6000 A thickness range have shown excellent lubricating properties, when sputtering parameters and substrate conditions are properly selected and precisely controlled. The lubricating properties of sputtered MoS2 films are strongly influenced by their crystalline-amorphous structure, morphology and composition. The coefficient of friction can range from 0.04 which is effective lubrication to 0.4 which reflects an absence of lubricating properties. Visual screening and slight wiping of the as-sputtered MoS2 film can identify the integrity of the film. An acceptable film displays a black-sooty surface appearance whereas an unacceptable film has a highly reflective, gray surface and the film is hard and brittle.

Spalvins, T.↗

NASA NTRS1990

Plasma-assisted physical vapor deposition surface treatments for tribological control

In any mechanical or engineering system where contacting surfaces are in relative motion, adhesion, wear, and friction affect reliability and performance. With the advancement of space age transportation systems, the tribological requirements have dramatically increased. This is due to the optimized design, precision tolerance requirements, and high reliability expected for solid lubricating films in order to withstand hostile operating conditions (vacuum, high-low temperatures, high loads, and space radiation). For these problem areas the ion-assisted deposition/modification processes (plasma-based and ion beam techniques) offer the greatest potential for the synthesis of thin films and the tailoring of adherence and chemical and structural properties for optimized tribological performance. The present practices and new approaches of applying soft solid lubricant and hard wear resistant films to engineering substrates are reviewed. The ion bombardment treatments have increased film adherence, lowered friction coefficients, and enhanced wear life of the solid lubricating films such as the dichalcogenides (MoS2) and the soft metals (Au, Ag, Pb). Currently, sputtering is the preferred method of applying MoS2 films; and ion plating, the soft metallic films. Ultralow friction coefficients (less than 0.01) were achieved with sputtered MoS2. Further, new diamond-like carbon and BN lubricating films are being developed by using the ion assisted deposition techniques.

Spalvins, Talivaldis↗

NASA NTRS1989

Interfacial analysis of tribological systems containing molybdenum disulfide and iron using XPS and CEMS

In the present evaluation of results from studies of the interfacial chemistry and morphology of a buried lubricant-substrate interface, specimens of increasing complexity that culminated with the effects of excess sulfur and defects were characterized by XPS and SEM, as well as conversion-electron Moessbauer spectroscopy (CEMS). In order to simulate sputtered systems, single crystals of MoS2 were damaged with Ar(+) bombardment and coated with Fe. Fe is found to react differently with MoS2 depending on surface treatments, surface defects, annealing treatments, and the presence of excess sulfur. The annealing temperature determines which compounds are formed, as well as the crystal habit and plane at the Fe-MoS2 interface.

Zabinski, J. S.↗

NASA NTRS1951

Preliminary Investigation of Molybdenum Disulfide-air-mist Lubrication for Roller Bearings Operating to DN Values of 1 x 10(exp 6) and Ball Bearings Operating to Temperatures of 1000 F

The effectiveness of molybdenum disulfide MoS2 as a bearing lubricant was determined at high temperature and at high speeds. A 1-inch-bore ball bearing operated at temperatures to 1000 F, a speed of 1725 rpm, and a thrust load of 20 pounds when lubricated only with MoS2-air mist. A 75-millimeter-bore cageless roller bearing, provided with a MoS2-syrup coating before operation, operated at DN values to 1 x 10(exp 6) with a load of 368 pounds.

BEARINGS, ANTI - FRICTION↗

NASA NTRS2000

Solid Lubrication Fundamentals and Applications

This chapter focuses attention on the friction and wear properties of selected solid lubricating films to aid users in choosing the best lubricant, deposition conditions, and operational variables. For simplicity, discussion of the tribological properties of concern is separated into two parts. The first part of the chapter discusses the different solid lubricating films selected for study including commercially developed solid film lubricants: (1) bonded molybdenum disulfide (MoS2), (2) magnetron-sputtered MoS2, (3) ion-plated silver, (4) ion-plated lead, (5) magnetron-sputtered diamondlike carbon (MS DLC), and (6) plasma-assisted, chemical-vapor-deposited diamondlike carbon (PACVD DEC) films. Marked differences in the friction and wear properties of the different films resulted from the different environmental conditions (ultrahigh vacuum, humid air, and dry nitrogen) and the solid film lubricant materials. The second part of the chapter discusses the physical and chemical characteristics, friction behavior, and endurance life of the magnetron-sputtered MoS2 films. The role of interface species and the effects of applied load, film thickness, oxygen pressure, environment, and temperature on the friction and wear properties are considered.

Miyoshi, Kazuhisa↗

NASA NTRS2005

High Resolution Spectroscopy And Timing Of The Isolated Neutron Star RBS 1774

The 2004 May 31 XMM-Newton observation was reprocessed using SASv6.0.0 and times of high background were filtered out. The net exposure time remaining was 23 ks. The source was clearly detected in MOS1, MOS2 and PN chips. We performed both timing and spectroscopic analysis on the data. We performed a spectral analysis by fitting data from the three EPIC detectors simultaneously, finding that the broadband spectrum can be represented by a single absorbed blackbody, with kT = 0.10 keV. The fitting revealed the presence of an absorption feature at 0:7 keV, but the data did have enough resolution to allow us to discriminate between an absorption line and an edge. We also tested magnetized models of Pavlov et a1 and Zavlin et al, but found that fits with these models were considerably worse than with a blackbody. For the timing analysis, we extracted the counts within a 3000 radius aperture in both PN and MOS 1 and MOS2 but with the aperture truncated by a chord where it approached the edge of the CCD window in each case: this maximized the counts while avoiding any edge effects. We analyzed PN, MOSl and MOS2 data both individually and combined using the Maximum Likelihood Periodogram technique of Zane et al. (2002) and Cropper et al. (2004). Periods from 10000 s to 30 ms were searched, ensuring that in each case the period grid was 2.5 times better sampled than the Nyquist frequency. The search revealed a significant period at 9.437s. Taken overall, we found the characteristics of RBS 1774 to be remarkably similar to those of another X-ray faint isolated neutron stars. These results were written up for the Astrophysical Journal, and the paper has recently been accepted for publication.

Mushotzky, Richard↗

NASA NTRS2010

An Evaluation of Liquid, Solid, and Grease Lubricants for Space Mechanisms Using a Spiral Orbit Tribometer

We present the findings of the test program performed by The European Space Tribology Laboratory (ESTL) to evaluate the performance (friction and lifetime) of a number of space lubricants under vacuum using a Spiral Orbit Tribometer (SOT). Focus was given to a comparison of various popular space oils, a comparison study between the old and new MAPLUB grease formulations, and the performance of commonly used solid lubricants under various conditions. Tests demonstrated that the lifetimes of hydrocarbon NYE oils 2001 & 2001A outperformed those of the perfluroropolyalkylether (PFPE) oils Fomblin Z25 & Z60, though these pairs displayed similar behavior. This relationship was also generally seen for greases; with the lifetimes of the multiple alkylated cyclopentane (MAC)-based greases being extended in comparison to the PFPE-based greases. Testing on greases also demonstrated similar performance between the old (-a) and new (-b) formulations when considering PFPE-based MAPLUB greases, and indeed for all tested PFPE-based non-MAPLUB greases, but significantly shorter lifetimes for the new formulations when considering MAC-based MAPLUB greases. MAPLUB MAC greases containing molybdenum disulphide (MoS2) thickener were also found to display reduced lifetimes. For solid lubricants, lead displayed significantly extended lifetimes over MoS2, speculated to be caused by redistribution of lead from the ball onto all contact surfaces during the test. Friction coefficients were seen to be some 2.5x higher for lead than for MoS2 under similar conditions, a result that corresponds well with conventional bearing tests. The work described was performed under contract for the European Space Agency as part of the Tribology Applications Program, with all funding for testing and apparatus provided by European Space Agency (ESA).

Buttery, Michael↗

DOE OSTI2025

All 2D Material Printed Diodes and Circuits on Paper for Sustainable Electronics

Sustainable electronics aim to reduce environmental impact by using ecofriendly materials, energy-efficient manufacturing, and recyclable components. However, existing approaches rely on complex, resource-intensive methods, rare metals, or nanomaterials with limited stability as well as plastic substrates, raising sustainability issues. Solution-processed two-dimensional (2D) materials offer a promising alternative: water-based and biocompatible conductive, semiconductive, and insulating 2D material inks can be produced with scalable techniques and are suitable for the fabrication of fully printed devices on low-cost and biodegradable paper substrates. However, 2D material only and fully printed diodes on paper have not yet been reported. Here, we demonstrate fully inkjet-printed 2D material-based diodes on paper using metal-insulator-semiconductor and metal-insulator-metal-semiconductor architectures. Water-based graphene and MoS2 inks, prepared by liquid-phase exfoliation, are used for the metallic and insulating films, while electrochemical exfoliation is used to produce the semiconducting MoS2 ink. The highest forward-to-reverse current ratio obtained is 330 (at ±2 V), while the forward current density is 1 mA/cm2 (at 1 V), making the diode performance comparable to the best solution-processed diodes reported so far. However, in contrast to previous works, fabrication occurs entirely at room temperature and ambient pressure, without using high-pressure sputtering, thermal evaporation, and any precious metal ink. The devices maintain stable performance under bending up to strain of 4% over 10,000 cycles. Finally, the diodes are successfully integrated with other 2D-material based electrical components to realize fully printed RC circuits, differentiators, integrators, and AC-to-DC converters onto paper, hence demonstrating the suitability of our approach for sustainable and disposable integrated circuits.

2D materials↗

DOE OSTI2025

Multiple Carrier Generation at an Exceptionally Low Energy Threshold

Multiple carrier generation (MCG), a process wherein two or more carriers are generated from a single high-energy absorbed photon, holds immense promise for quantum sensing, metrology, low-threshold lasers, and photovoltaics. Despite its potential, MCG has faced obstacles such as low efficiency and a high threshold photon energy at least twice the band gap (2?Eg) of the semiconductor, limiting its application only to a class of materials with low Eg. Here, we present a new approach that overcomes this limitation by leveraging carrier-donor scattering to excite secondary electrons from donor states strategically positioned below the conduction band. Our method relies on strong Coulomb interaction, reduced dielectric screening, slow hot carrier cooling, and strictly follows the energy conservation rules. We experimentally demonstrated this idea in a model system of monolayer (1L) MoS2 by exploiting electron-donating chalcogen vacancy states. We observed an exceptionally low MCG threshold of ~1.12?Eg for the first time in 1L MoS2. Remarkably, the quantum yield can be further increased to >3 by increasing the photon energy to 1.65?Eg, representing a substantial advancement over existing methods. Our findings extend the horizon of MCG into next-generation high-performance optoelectronic devices with an on-demand operating spectral range spanning from infrared to ultraviolet.

CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS↗

NASA NTRS1972

Sputtering: A vacuum deposition method for coating material

The sputtering process is described in terms of its features: versatility, momentum transfer, configuration of target, precise controls and the relatively slow deposition rate. Sputtered films are evaluated in terms of adherence, coherence, and internal stresses. The strong adherence is attributed to the high kinetic energies of the sputtered material, sputter etched (cleaned) surface, and the submicroscopic particle size. An illustration is a sputtered solid film lubricant such as MoS2. Friction tests were conducted on a thin, 2000 A deg thick MoS2 film. These films are very dense and without observable pinholes, and the particle to particle cohesion is strong. Tolerances (film thickness) can be controlled to a millionth of a centimeter. Very adherent films of sputtered Teflon can be deposited in a single operation on any type of material (metal, glass, paper) and on any geometrical configuration with a dense adherent film.

Spalvins, T.↗

NASA NTRS1972

Lubricating characteristics of polyimide bonded graphite fluoride and polyimide thin films

A friction and wear life study was conducted on the use of a polyimide (PI) varnish as a binder for the solid lubricant, graphite fluoride (CF(1.1))N. Also studied were the lubricating properties of PI thin films with no solid lubricant additives. For comparison, similar experiments on PI-bonded MoS2 and burnished films of MoS2 or (CF(li))N were conducted. The best results were obtained with the PI-bonded (CF(1.1))N films. The polyimide thin films (with no solid lubricant additives) did not lubricate well at 25 C; however, when heated to 100 C, low friction and long wear lives were obtained.

Fusaro, R. L.↗

NASA NTRS1972

Lubricating characteristics of polyimide bonded graphite fluoride and polyimide thin films.

A friction and wear life study was conducted on the use of a polyimide (PI) varnish as a binder for the solid lubricant, graphite fluoride (CF sub 1.1) sub n. Also studied were the lubricating properties of PI thin films with no solid lubricant additives. For comparison, similar experiments on PI-bonded MoS2 and burnished films of MoS2 or (CF sub 1.1) sub n were conducted. The best results were obtained with the PI-bonded (CF sub 1.1) sub n films. The polyimide thin films (with no solid lubricant additives) did not lubricate well at 25 C; however, when heated to 100 C, low friction and long wear lives were obtained.

Fusaro, R. L.↗

NASA NTRS1974

Start-stop testing of two self-acting air-lubricated spiral groove thrust bearing coatings

Start-stop tests were conducted on air-lubricated spiral-groove thrust bearings. Application of a matrix-bonded molybdenum disulfide (MoS2) coating over a porous chrome oxide coating resulted in significantly lower friction, compared to bearings coated with chrome oxide only. The MoS2 coated bearing sustained 15,000 start-stop cycles at a maximum of 3600 rpm. Each cycle was 15 seconds on, 30 seconds off. The chrome oxide coated bearing failed by local welding after 2030 cycles. Both types of coatings exhibited early failures under higher thrust loads when operating films were insufficient to sustain the load without overheating.

Dunfee, J. D.↗

NASA NTRS1975

Organopolysiloxane-bonded graphite fluoride as a solid lubricant

A study was conducted on the lubricating properties of organopolysiloxane-bonded graphite fluoride (CF sub 1.1) sub n films. The effects of temperature, atmosphere, composition of organopolysiloxane, and burnishing additional (CF sub 1.1) sub n powder onto the film surface were studied. For comparison, similar experiments were conducted on organopolysiloxane-bonded MoS2 films. The results are equivalent for both films, except that in a moist air environment the wear lives of the films formulated with (CF sub 1.1) sub n are up to 10 times longer than the wear lives of the MoS2-formulated films. Comparison to other (CF sub 1.1) sub n films showed organopolysiloxane films to give better lubrication results than hand-burnished (CF sub 1.1) sub n films but not as good as polyimide-bonded (CF sub 1.1) sub n films.

Fusaro, R. L.↗

NASA NTRS1977

Microstructural and wear properties of sputtered carbides and silicides

Sputtered Cr3C2, Cr3Si2, and MoSi2 wear-resistant films (0.05 to 3.5 microns thick) were deposited on metal and glass surfaces. Electron transmission, electron diffraction, and scanning electron microscopy were used to determine the microstructural appearance. Strong adherence was obtained with these sputtered films. Internal stresses and defect crystallographic growth structures of various configurations within the film have progressively more undesirable effects for film thicknesses greater than 1.5 microns. Sliding contact and rolling element bearing tests were performed with these sputtered films. Bearings sputtered with a duplex coating (0.1-micron-thick undercoating of Cr3Si2 and subsequently 0.6-micron coating of MoS2) produced marked improvement over straight MoS2 films.

Spalvins, T.↗